The techniques for driving electronically switched multi-phase brushless motors commonly include forcing currents through the phase windings of the motor according to a voltage or current mode control and using Hall effect sensors for synchronizing the switchings. Depending on the number of phases, windings, and poles of the rotor, the driving system must command the phase switchings according to a proper sequential scheme. This scheme must be closely synchronized with the rotor's position to maximize efficiency and minimize ripple.
Frequently, in a three-phase motor with a rotor having two pairs of poles, the switching sequence has six phases, each phase being 60 electrical degrees. One of the techniques used for determining the rotor's instantaneous position is that of installing three Hall effect sensors. These sensors are commercially available and provide for three logic signals (codes) whose logic combination permits establishing the rotor's position and the correct phase to be excited.
In general, the decoding conventions of the logic signals produced by such sensors consider different schemes. These schemes depend upon the electrical sensors' phasing in terms of electrical degrees of separation, which in turn depends on the sensors' physical positions and the number of poles on the rotor. Therefore, by changing the sensors' physical positions and the number of rotor poles, there will be different sensor phasing, for example, of 60, 120, 240 and 300 electrical degrees.
Normally, the integrated devices installed in brushless motors for decoding signals produced by the Hall effect sensors and for processing the rotor's angular position (which are commonly used to realize the electronic driving systems) contemplate the possibility of pre-establishing which sensor phasing scheme must be selected for correctly decoding and processing the sensor signals. In practice, known devices dedicate one or more pins for presetting the decoding and processing circuit. Through these selection pins (or circuit nodes), an integrated circuit can be configured to decode signals originating from Hall effect sensors positioned at intervals of 120 electrical degrees, 60 electrical degrees, or even 240 or 300 electrical degrees.
An example of a commercially available decoding device is the MC33033 by Motorola. In this device, the selection of the actual angular separation between sensors of 60 or 120 electrical degrees is made through the pins 3 and 18.
There is a need for a method and corresponding decoding circuit for decoding the logic signals produced by three Hall effect sensors relating to the instantaneous position of a rotor of a three-phase brushless motor. Such a decoding method and detection circuit should be capable of self recognizing, depending on the direction of rotation, the actual sensor positions, at intervals of either 60, 120, 300 or 240 electrical degrees, without the need for supplying such phasing information to the decoding circuit. Such a decoding method and circuit will permit the use of common devices without dedicating pins to allow for pre-setting phasing information, thus simplifying the manufacture of control systems for one or more brushless motors.